The present invention relates, in general, to a load sharing mechanism for power transmissions and in particular to a load sharing mechanism for gear transmission with stepped gears.
Rotary wing aircraft typically uses high-speed turbine engine to drive the rotor or propeller. A main gear transmission between the engine the rotor is necessary to transmit engine power while reducing the engine speed to the appropriate rotor speed. The main gear transmission is usually the heaviest subsystem in the drive train of the aircraft. Increasing power throughput and reducing the weight of the transmission is very desirable for modern rotary wing aircraft.
One effective way to improve power density is to divide the input torque from the gas turbine engine into multiple paths. Each path uses a smaller individual gear member which leads to an overall transmission design that is lighter in weight, compact in size and has smaller gear face width due to the lower loads in each gear mesh. The smaller but numerous gears also require smaller bearings which have increased life span due to less applied torque.
One embodiment of a power dense planetary gear transmission consists of a compound planetary gear-train having a set of stepped planet gears. Each stepped planet gear includes a large planet gear and a small drive planet pinion. The stepped planet gears may have flexible or pivot-able shaft. A set of small and simple idler planet pinions supported by a planet carrier are employed to share the torque, distributing load carried by the transmission among the drive planet pinions and the idler planet pinions. The idler planet pinions have non-floating shaft with respect to the planet carrier.
Alternative transmission configurations such as split-torque face gear transmission may also be utilized, where a stepped gear is used to drive a primary face gears and two idler face gears that sandwich the primary face gear. The stepped gears have fixed shaft. Small idler gears were used as crossover gears to provide multiple power paths to share the load. Similarly, the idler gears also have fixed shafts.
Load sharing mechanisms may be disposed within a power dense planetary gear transmission. These load sharing mechanisms may include a stepped gear cluster having a large gear and a small drive gear. The small drive gear meshes with two reaction gears, and the load sharing is achieved through a mechanical mechanism where a support structure of stepped gear cluster is devised utilizing a single pivoting support bearing which is selectively positioned between the large and small gears of the stepped gear cluster. The support structure and position of the pivoting support bearing allows the tangential forces of the small drive planet gear at mesh points with two reaction gears to be partitioned to achieve a desired load sharing ratio between the two reaction gears edge loading may occur if the gear teeth were not properly crowned.
Accordingly, it would be advantageous to provide a flexible support structure in a gear transmission that allows for partitioning of a load between two reaction gears as desired, and for partitioning of a load between cluster support bearings to optimize the load distribution among drive planet pinions and idler planet pinions, and to maintain parallel gear engagement. In doing so, the maximum load capacity can be achieved.